As conventional motor stators designed to enhance yield of a core material used for manufacturing laminated cores, one of the structures hitherto known is made of strip-like core members die-cut from the core material which are laminated, changed into an annular shape after a coil is wound on the strip-like core members, and two ends of which are joined by welding (refer to patent literature 1, for example).
FIG. 5 is a plan view of a stator core of a conventional permanent-magnet brushless motor after the stator core is bent. Stator core 11 is constructed of a plurality of core pieces 11a which are linked by intermediate thin-wall portions 11b and laminated together. Also, each of core pieces 11a is provided with tooth 13. Before being bent, stator core 11 has flat butt surface 15 and tongued-grooved portion 16 formed at each of two ends thereof. Motor stator 10 is constructed by bending thin-wall portions 11b of stator core 11 to form stator core 11 into an annular shape, joining the two ends of stator core 11 by welding, and forming slots 14 between adjoining teeth 13. Welded portion 17 in outer periphery 10a is located at center line 18 in a radial direction of slot 14.
In the conventional art discussed above, however, there is a problem that an efficiency of the motor decreases due to an increase in iron loss as a result of the welding of the ends of the core members, which breaks insulation films on both surfaces of the core members at the welded portion, electrically conducted between the core members, and then increases an eddy current.
PTL 1: Unexamined Japanese Patent Publication No. 2009-33874